Revolving algal biofilm photobioreactor systems and methods

ABSTRACT

An algal growth system can include a flexible sheet material, where the flexible sheet material can be configured to facilitate the growth and attachment of algae. The algal growth system can include a plurality of shafts, where the plurality of shafts can be associated with and support the flexible sheet material, a gear system, a drive motor, where the drive motor can be coupled with the gear system, where the drive motor can actuate the gear system and the plurality of shafts such that the flexible sheet material can be actuated, a fluid reservoir, where the flexible sheet material can be configured to pass through the fluid reservoir, a contacting liquid, and a liquid phase and a gaseous phase.

REFERENCE TO RELATED APPLICATIONS

The present application claims the priority benefit of U.S. provisional patent application Ser. No. 61/783,737, filed Mar. 14, 2013, and hereby incorporates the same application herein by reference in its entirety.

TECHNICAL FIELD

Embodiments of the technology relate, in general, to biofilm technology, and in particular to a revolving algal biofilm photobioreactor (RABP) for simplified biomass harvesting.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be more readily understood from a detailed description of some example embodiments taken in conjunction with the following figures:

FIG. 1 depicts a flow chart illustrating considerations that may need to be addressed by example embodiments described herein.

FIG. 2 depicts a top view of microalgae being grown on polystyrene foam.

FIG. 3 depicts a perspective view of an example embodiment of a revolving algal biofilm photobioreactor.

FIG. 4 depicts a schematic front view of the revolving algal biofilm photobioreactor shown in FIG. 3.

FIG. 5 depicts a top view of microalgae being grown on a variety of materials.

FIG. 6 depicts a bar chart of harvesting frequencies for an algal strain.

SUMMARY

An algal growth system can include a flexible sheet material, where the flexible sheet material can be configured to facilitate the growth and attachment of algae. The algal growth system can include a plurality of shafts, where the plurality of shafts can be associated with and support the flexible sheet material, a gear system, where the gear system can be coupled with the plurality of shafts, a drive motor, where the drive motor can be coupled with the gear system, where the drive motor can actuate the gear system and the plurality of shafts such that the flexible sheet material can be actuated, a fluid reservoir, where the flexible sheet material can be configured to pass through the fluid reservoir during operation of the algal growth system harvesting system, a contacting liquid, where the contacting liquid can be retained within the fluid reservoir and can include nutrients that can facilitate the growth of the algae, and a liquid phase and a gaseous phase, where the liquid phase can include rotating the flexible sheet material through the contacting liquid retained in the fluid reservoir and the gaseous phase can include rotating the flexible sheet material through gaseous carbon dioxide.

A method of growing algae can include the step of providing an algal growth system that can include a flexible sheet material, where the flexible sheet material can be configured to facilitate the growth and attachment of algae, a plurality of shafts, where the plurality of shafts can be associated with and support the flexible sheet material, a gear system, where the gear system can be coupled with the plurality of shafts, a drive motor, where the drive motor can be coupled with the gear system, where the drive motor can actuate the gear system and the plurality of shafts such that the flexible sheet material can be substantially rotated, a fluid reservoir, where the flexible sheet material can be configured to pass through the fluid reservoir during operation of the algal growth system, and a contacting liquid, where the contacting liquid can be retained within the fluid reservoir and can include nutrients that can facilitate the growth of the algae. The method of growing algae can include the steps of rotating the flexible sheet material of the algal growth system through a liquid phase such that the flexible sheet material can pass through the contacting liquid retained in the fluid reservoir and the step of rotating the flexible sheet material of the algal growth system through a gaseous phase such that the flexible sheet material can pass through gaseous carbon dioxide. The method of growing algae can include the step of harvesting the algae from the flexible sheet material.

DETAILED DESCRIPTION

Various non-limiting embodiments of the present disclosure will now be described to provide an overall understanding of the principles of the structure, function, and use of the proficiency tracking systems and processes disclosed herein. One or more examples of these non-limiting embodiments are illustrated in the accompanying drawings. Those of ordinary skill in the art will understand that systems and methods specifically described herein and illustrated in the accompanying drawings are non-limiting embodiments. The features illustrated or described in connection with one non-limiting embodiment may be combined with the features of other non-limiting embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure.

Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” “some example embodiments,” “one example embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with any embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” “some example embodiments,” “one example embodiment, or “in an embodiment” in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

Traditionally, algae are grown in open raceway ponds or enclosed photobioreactors, where algae cells are in suspension and are harvested through sedimentation, filtration, or centrifugation. Due to the small size (3-30 μm) of algae cells and the dilute algae concentration (<1% w/v), gravity sedimentation of suspended cells often takes a long time in a large footprint settling pond. Filtration of algal cells from the culture broth can result in filter fouling. Centrifugation can achieve high harvest efficiency; however, the capital investment and operational cost for a centrifugation system can be prohibitively expensive. Due to these drawbacks, an alternative method for harvesting and dewatering algae biomass may be advantageous.

Described herein are example embodiments of revolving algal biofilm photobioreactor systems and methods that can simplify biomass harvesting. In one example embodiment, systems and methods can provide cost effective harvesting of algae biomass. In some embodiments, systems and methods can be used to produce algae for both biofuel feedstock and aquacultural feed sources. In some embodiments, algal cells can be attached to a material that can be rotated between a nutrient-rich liquid phase and a carbon dioxide rich gaseous phase such that alternative absorption of nutrients and carbon dioxide can occur. The algal cells can be harvested by scrapping from the surface to which they are attached, which can eliminate harvest procedures commonly used in suspension cultivation systems, such as sedimentation or centrifugation. It will be appreciated that systems and methods described herein can be combined with sedimentation, centrifugation, or any other suitable processes.

The examples discussed herein are examples only and are provided to assist in the explanation of the apparatuses, devices, systems and methods described herein. None of the features or components shown in the drawings or discussed below should be taken as mandatory for any specific implementation of any of the apparatuses, devices, systems or methods unless specifically designated as mandatory. For ease of reading and clarity, certain components, modules, or methods may be described solely in connection with a specific figure. Any failure to specifically describe a combination or sub-combination of components should not be understood as an indication that any combination or sub-combination is not possible. Also, for any methods described, regardless of whether the method is described in conjunction with a flow diagram, it should be understood that unless otherwise specified or required by context, any explicit or implicit ordering of steps performed in the execution of a method does not imply that those steps must be performed in the order presented but instead may be performed in a different order or in parallel.

Example embodiments described herein can mitigate air and water pollution while delivering high value bio-based products and animal feeds from microalgae. Example embodiments of RABP technology can play a critical role in creating an algal culture system that can economically produce algae biomass for, for example, biofuel production and aquacultural feed production. Microalgae may have a significant impact in the renewable transportation fuels sector. Example embodiments can grow microalgae that can be used in biofuel production with a low harvest cost. Algae, if produced economically, may also serve as a primary feed source for the US aquaculture industry.

Example systems and methods can include developing a biofilm-based microalgae cultivation system (RABP) that could be widely adapted by the microalgae industry for producing, for example, fuels and high value products. Over the past few years microalgae has been rigorously researched as a promising feedstock for renewable biofuel production. Microalgae use photosynthesis to transform carbon dioxide and sunlight into energy. This energy is stored in the cell as oils, which have a high energy content. The oil yield from algae can be significantly higher than that from other oil crops. Algae oil can generally be easily converted to biodiesel and could replace traditional petroleum-based diesel. In addition to fuel production, microalgae have also been rigorously researched for the potential to produce various high value products such as animal feed, omega-3 polyunsaturated fatty acids, pigments, and glycoproteins.

Referring to FIG. 1, in spite of the strong potential of microalgae in various applications, the high cost of algae production can still be the major limitation in industrial scale operation. According to the United States Department of Energy's final report on the Aquatic Species Program and the recent National Algal Biofuel Technology Roadmap, there are three main areas that may need to be focused on in order to make algae cultivation economically viable, including strain development, control of contamination by native species, and reducing the high cost of biomass harvesting and dewatering. Example embodiments may minimize the cost associated with biomass harvesting and dewatering of algal cells from an aqueous culture system.

Generally, research on algae cultivation is done using suspended algae culture. This culture method can have drawbacks including the issue with harvesting. Example embodiments can promote a simple economical harvesting method. Example embodiments can include a mechanized harvesting system, which can remove concentrated algae in-situ from an attachment material and can minimize the amount of de-watering needed post-harvest. Example embodiments can optimize gas mass transfer, where growth in an enclosed greenhouse 40 may provide the ability to increase CO2 concentration inside the reactor. Generally, at higher CO2 concentrations, the growth rate of algae will increase. Example embodiments can utilize minimal growth medium, where the triangular design in example embodiments may reduce the chemical costs of growth medium and may reduce the total water needed for the growth. In one embodiment, such advantages may be accomplished by submerging only the lowest elevated corner of a triangle system needs into the medium.

Referring to FIG. 2, microalgae can be grown on the surface of polystyrene foam. FIG. 2 illustrates how algae can be harvested by scraping the surface of the foam. The mechanical separation can result in biomass with water content similar to centrifuged samples and the residual biomass left on the surface can serve as an ideal inoculum for subsequent growth cycles. However, such systems can be limited by the use of polystyrene foam which is not a renewable and environmental friendly material. The rigidity of the styrene foam may also limit its application in embodiments of rotational systems and methods described herein.

Referring to FIGS. 3 and 4, an example embodiment of a revolving algal biofilm Photobioreactor (RABP) 10, in which the algal cells 18 can be attached to a solid surface of a supporting material 12, is disclosed. The system can keep the algal cells fixed in place and can bring nutrients to the cells, rather than suspend the algae in a culture medium. As shown in FIGS. 3 and 4, algal cells can be attached to a material 12 that is rotating between a nutrient-rich liquid phase 15 and a CO2-rich gaseous phase 16 for alternative absorption of nutrients and CO2. The algal biomass can be harvested by scrapping the biomass from the attached surface with a harvesting squeegee 20 (FIG. 4) or other suitable device or system. In example embodiments, the naturally concentrated biofilm can be in-situ harvested during the culture process, rather than using an additional sedimentation or flocculation step for harvesting, for example. The culture can enhance the mass transfer by directly contacting algal cells with CO2 molecules in gaseous phase, where traditional suspended culture systems may have to rely on the diffusion of CO2 molecules from gaseous phase to the liquid phase, which may be limited by low gas-liquid mass transfer rate. Example embodiments may only need a small amount of water by submerging the bottom of the triangle 22 in liquid 14 while maximizing surface area for algae to attach. Example embodiments can be scaled up to an industrial scale because the system may have a simple structure and can be retrofit on existing raceway pond systems. Example embodiments can be used in fresh water systems and can be adapted to saltwater culture systems. For example, embodiments of this system can be placed in the open ocean instead of in a raceway pond reactor. In this example application, the ocean can naturally supply the algae with sufficient sunlight, nutrient, water, and CO2, which in turn may decrease operational costs.

Still referring to FIGS. 3 and 4, embodiments of the system can include a drive motor 24, a gear system 26 that can rotate drive shafts 28, drive shafts 28 that can rotate a flexible material 12, a flexible sheet material 12 that can rotate into contact with liquid 14 and can allow algae 18 to attach thereto. The motor 24 can include a gear system 26 or pulley system that can drive one or a plurality of shafts 28, where the shafts 28 can rotate the flexible sheet material 12 in and out of a contacting liquid 14, for example. Embodiments can also include a liquid reservoir 30, mister, water dripper, or any other suitable component or mechanism that can keep algae, which can be attached to the flexible sheet material 12, moist. Embodiments can include any suitable scraping system, vacuum system or mechanism for harvesting the algae 18 from the flexible sheet material 12.

In an example embodiment, a generally triangular system 22 can be provided. Such a configuration can be beneficial in maximizing the amount of sunlight algae is exposed to. However versions of the system can be designed, for example, in any configuration that includes a “sunlight capture” part 32 which can be exposed to air and sunlight, and a “nutrient capture” part 34 which can be submerged into a nutrient solution. A straight vertical design is contemplated, which may be the simplest and most cost efficient design because such a system may minimize the amount of wasted space and may maximize the amount of algae produced in a small area by growing this system vertically. Alternative designs can include a straight vertical reactor, a reactor that is straight but slightly angled to provide more surface area for sunlight to hit, a cylindrical reactor, or a square shaped reactor.

Referring to FIG. 5, any suitable material 12, such as any suitable flexible fabric, can be used with the systems and methods described herein to grow any suitable material. For example, the microlaga Chlorella, such as Chlorella vulgaris can be grown on materials such as, muslin cheesecloth, armid fiberglass, porous PTFE coated fiberglass, chamois, vermiculite, microfiber, synthetic chamois, fiberglass, burlap, cotton duct, velvet, Tyvek, poly-lactic acid, abrased poly-lactic acid, vinyl laminated nylon, polyester, wool, acrylic, lanolin, woolen, cashmere, leather, silk, lyocell, hemp fabric, Spandex, polyurethane, olefin fibre, polylactide, Lurex, carbon fiber, and combinations thereof.

It will be appreciated that any suitable algal strain 18 (including cyanobacteria) as well as fungal strains, such as strains that can be used in aquaculture feed, animal feed, nutraceuticals, or biofuel production can be used. Such strains can include Nannochloropsis sp., which can be used for both biofuel production and aquacultural feed; Scenedesmus sp., a green microalga that can be used in wastewater treatment as well as for fuel production feedstock; Haematococcus sp, which can produce a high level of astaxanthin; Botryococcus sp. a green microalga with high oil content; Spirulina sp. a blue-green alga with high protein content; Dunaliella sp. a green microalga containing a large amount of carotenoids; a group of microalgae species producing a high level of long chain polyunsaturated fatty acids can include Arthrospira, Porphyridium, Phaeodactylum, Nitzschia, Crypthecodinium and Schizochytrium. Any suitable parameter, including gaseous phase CO2 concentration, harvesting frequency, the rotation speed of the RABP reactor, the depth of the biofilm harvested, the ratio of submerged portion to the air-exposure portion of the RABP reactor, or the gap between the different modules of the RABP system can be optimized for any suitable species.

Referring to FIG. 6, any harvesting schedule can be used in accordance with example embodiments described herein. The mechanism of harvesting biomass from the biofilm can be, for example, scraping or vacuum. Biomass productivity may vary by species and any suitable harvesting time is contemplated to maximize such productivity. For example, as shown in FIG. 6, of this specific species as a function of harvesting time by growing the algae on a RABP system then harvesting the cells at different durations. As shown in FIG. 6, for Chlorella the optimal harvest frequency may be every 7 days. In example embodiments, managing other parameters such as CO2 concentration and nutrient loading may also impact algal growth performance.

In various embodiments disclosed herein, a single component can be replaced by multiple components and multiple components can be replaced by a single component to perform a given function or functions. Except where such substitution would not be operative, such substitution is within the intended scope of the embodiments.

Some of the figures can include a flow diagram. Although such figures can include a particular logic flow, it can be appreciated that the logic flow merely provides an exemplary implementation of the general functionality. Further, the logic flow does not necessarily have to be executed in the order presented unless otherwise indicated. In addition, the logic flow can be implemented by a hardware element, a software element executed by a computer, a firmware element embedded in hardware, or any combination thereof.

The foregoing description of embodiments and examples has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the forms described. Numerous modifications are possible in light of the above teachings. Some of those modifications have been discussed, and others will be understood by those skilled in the art. The embodiments were chosen and described in order to best illustrate principles of various embodiments as are suited to particular uses contemplated. The scope is, of course, not limited to the examples set forth herein, but can be employed in any number of applications and equivalent devices by those of ordinary skill in the art. Rather it is hereby intended the scope of the invention to be defined by the claims appended hereto. 

We claim:
 1. An algal growth system comprising: (a) a flexible sheet material, the flexible sheet material being configured to facilitate the growth and attachment of algae; (b) a plurality of shafts, wherein the plurality of shafts are associated with and support the flexible sheet material; (c) a gear system, wherein the gear system is coupled with the plurality of shafts; (d) a drive motor, the drive motor being coupled with the gear system, wherein the drive motor actuates the gear system and the plurality of shafts such that the flexible sheet material is actuated; (e) a fluid reservoir, wherein the flexible sheet material is configured to pass through the fluid reservoir during operation of the algal growth system harvesting system; (f) a contacting liquid, wherein the contacting liquid is retained within the fluid reservoir and includes nutrients that facilitate the growth of the algae; and (g) a liquid phase and a gaseous phase, wherein the liquid phase comprises rotating the flexible sheet material through the contacting liquid retained in the fluid reservoir and the gaseous phase comprises rotating the flexible sheet material through gaseous carbon dioxide.
 2. The algal growth system of claim 1, further comprising a harvesting mechanism.
 3. The algal growth system of claim 1, wherein the harvesting mechanism is a squeegee.
 4. The algal growth system of claim 1, wherein the flexible sheet material is selected from the group consisting of cheesecloth, fiberglass, porous PTFE coated fiberglass, chamois, vermiculite, microfiber, synthetic chamois, burlap, cotton duct, velvet, poly-lactic acid, abrased poly-lactic acid, vinyl laminated nylon, polyester, wool, acrylic, lanolin, woolen, cashmere, leather, silk, lyocell, hemp fabric, polyurethane, olefin fibre, polylactide, and carbon fiber.
 5. The algal growth system of claim 1, wherein the algae is selected from the group consisting of Nannochloropsis, Scenedesmus, Haematococcus, Botryococcus, Spirulina, Dunaliella, Arthrospira, Porphyridium, Phaeodactylum, Nitzschia, Crypthecodinium and Schizochytrium.
 6. The algal growth system of claim 1, wherein the algal growth system has a substantially triangular configuration having a lower corner, a first upper corner, and a second upper corner.
 7. The algal growth system of claim 6, wherein the lower corner of the algal growth system is positioned within the fluid reservoir.
 8. The algal growth system of claim 1, further comprising an enclosed greenhouse.
 9. The algal growth system of claim 8, wherein the enclosed greenhouse has a higher carbon dioxide concentration than the atmosphere.
 10. The algal growth system of claim 1, wherein the drive motor is configured to rotate the flexible sheet material on a predetermined schedule.
 11. The algal growth system of claim 1, wherein the flexible sheet material is a biofilm.
 12. The algal growth system of claim 1, wherein the flexible sheet material is configured to grow and retain the algae until the algae is physically removed.
 13. The algal growth system of claim 1, wherein the algal growth system is configured for industrial use.
 14. A method of growing algae comprising the steps of: providing an algal growth system comprising; (a) a flexible sheet material, the flexible sheet material being configured to facilitate the growth and attachment of algae; (b) a plurality of shafts, wherein the plurality of shafts are associated with and support the flexible sheet material; (c) a gear system, wherein the gear system is coupled with the plurality of shafts; (d) a drive motor, the drive motor being coupled with the gear system, wherein the drive motor actuates the gear system and the plurality of shafts such that the flexible sheet material is substantially rotated; (e) a fluid reservoir, wherein the flexible sheet material is configured to pass through the fluid reservoir during operation of the algal growth system; and (f) a contacting liquid, wherein the contacting liquid is retained within the fluid reservoir and includes nutrients that facilitate the growth of the algae rotating the flexible sheet material of the algal growth system through a liquid phase such that the flexible sheet material passes through the contacting liquid retained in the fluid reservoir; rotating the flexible sheet material of the algal growth system through a gaseous phase such that the flexible sheet material passes through gaseous carbon dioxide; and harvesting the algae from the flexible sheet material.
 15. The method of growing algae of claim 14, wherein the algal growth system further comprises an enclosed greenhouse.
 16. The method of growing algae of claim 14, wherein the algal growth system has a substantially triangular configuration.
 17. The method of growing algae of claim 14, wherein the algae is selected from the group consisting of Nannochloropsis, Scenedesmus, Haematococcus, Botryococcus, Spirulina, Dunaliella, Arthrospira, Porphyridium, Phaeodactylum, Nitzschia, Crypthecodinium and Schizochytrium.
 18. The method of growing algae of claim 14, wherein the flexible sheet material is selected from the group consisting of cheesecloth, fiberglass, porous PTFE coated fiberglass, chamois, vermiculite, microfiber, synthetic chamois, burlap, cotton duct, velvet, poly-lactic acid, abrased poly-lactic acid, vinyl laminated nylon, polyester, wool, acrylic, lanolin, woolen, cashmere, leather, silk, lyocell, hemp fabric, polyurethane, olefin fibre, polylactide, and carbon fiber.
 19. The method of growing algae of claim 14, wherein the algal growth system is configured for industrial use.
 20. The method of growing algae of claim 14, further comprising the step of rotating the algal growth system according to a predetermined schedule. 